Field of the Invention
The invention relates to field device with an input unit.
Background of the Invention
The present invention is a field device with an input unit, with the input unit comprising a first number of switch elements to generate first input signals and a second number of sensor elements, allocated to the switch elements and allowing magnetic actuation, to generate second input signals, with the second input signals being OR-linked to the first input signals.
Such field devices with input units are known from prior art, for example from DE 37 34 494, which describes a control device secured against explosion, in which one group of data input/scanning sites is allocated to a group of sensors that are aligned to the scanning sites and can be magnetically actuated. In this arrangement known from prior art one input key is respectively allocated to a magnetically actuated sensor and placed directly underneath it. When it is now necessary to enter data at an input unit arranged at the control device, which is arranged in a housing secured against explosion, this can occur via a permanent magnet using its magnetically operating sensors, which can be actuated. In this arrangement known from prior art it is relevant that the keys and the sensors allocated to the keys show a minimum distance, which is selected such that it is not shorter than the interfering distance of the sensors. The interfering distance is understood in the present application as the distance between two sensors at which any differentiation of entries made to these two sensors cannot be clearly distinguished.
Alternative options for actuating input units of field devices of prior art include, for example, a capacitive input, such as the ones used for modern smartphones and tablet PCs or the scanning of a field for infrared radiation. Capacitive inputs are however very limited at the distance, at which actuation occurs, and the scanning of fields for infrared radiation is very expensive with regards to calculation in embedded systems, as typically used in field devices. Both systems cannot be used here, or only to a limited extent. Furthermore, systems operating with infrared radiation are very susceptible to malfunction due to soiling.
FIG. 3 shows an input unit 1 for a field device known from prior art. The input unit 1 comprises four switch elements S1 to S4 arranged in a gap, with respectively a sensor element H1 to H4 being allocated thereto. The switch elements S1 to S4 and the allocated sensor elements H1 to H4 are electrically switched parallel such that respectively by actuating a switch element S1 to S4 or a sensor element H1 to H4 allocated to the switch element an input signal E1 to E4 can be issued. For example the first switch element S1 and the first sensor element H1 are switched parallel such that both an actuation of the first switch element S1 embodied as a sensor as well as an excitation of the first sensor element H1, embodied as a first Hall sensor, is possible generating the first input signal E1. For reasons of simplification, technically necessary pull-up resistors are not shown for the input signals E1 to E4. However they are functionally required and will be provided accordingly by one trained in the art.
The objective of the present invention is to improve a field device with an input unit such that a higher precision of input is yielded and a further miniaturization of the input unit is possible.
This objective is attained in a field device with the features disclosed herein below.